This invention relates in general to measuring devices and in particular to a new and useful portal type coordinate measuring machine.
The invention relates to a portal type coordinate machine in which the columns on both sides of the measuring table are disposed in ways so as to be movable lengthwise and firmly interconnected by a bridge accommodating the measuring head holder, and which, furthermore, has a measuring device each along the ways of both columns to indicate the position of the columns.
A coordinate measuring machine, in particular length measuring machine, of the above mentioned kind is known from German AS No. 22 48 194. This publication describes a solution of the problem when the two vertical columns are to be moved accurately in the associated ways along the measuring table in order to relocate both columns along the travel axis relative to a reference position, maintaining exactly the same distance. In can be learned from this German AS No. 22 48 194 that the above mentioned problem cannot be eliminated completely even when using expensive precision elements, for which reason there are provided, as a solution, on the ways of the columns two measuring devices whose output signals are compensated together with the output signal of a third measuing device. Each column of this known coordinate measuring machine is moved by means of an associated precision screw screwed into a nut with no, or little, friction. The respective nut is provided at the associated column. It is aligned axially with a large diameter hole in the associated column.
This hole is to assure that when the screw is turned, it does not touch the column. Known from German OS No. 31 50 978 is a portal type measuring machine which has a central guide rail. The portal is formed by two columns and the bridge. Installed in the feet of the columns are air bearings, by means of which the portal slides on the base plate. The portal drive is integrated in the housing and has two friction rolls acting upon the guide rail.